1. Technical Field
The present disclosure relates to an error amplification circuit to perform phase compensation, a control method for the error amplification circuit, and a switching regulator employing the error amplification circuit.
2. Description of the Background Art
In known exterior phase compensation methods for error amplifiers used in power supplies such as switching regulators and series regulators, typically a phase compensation circuit in which a phase compensation resistor and a phase compensation capacitor are connected in series is connected between a phase compensation terminal of an integrated circuit and a ground terminal However, the phase compensation terminal has parasitic capacitance (capacitor) and is connected to an error-voltage output terminal of an error amplifier. Therefore, the parasitic capacitance of the phase compensation terminal and an external phase compensation circuit are connected in parallel to the error-voltage output terminal of the error amplifier. A technique is known in which, by reducing impedance of the external phase compensation circuit compared to the parasitic capacitance of the phase compensation terminal, the output resistance of the error amplifier is reduced to a level suitable for the external phase compensation circuit.
FIG. 1 is a circuit diagram illustrating a configuration of a conventional error amplification 110a installed in a switching regulator 100. The error amplification circuit 110a includes an integrated circuit 110 and a phase compensation circuit COMP101. In addition, the integrated circuit 110 includes an error amplifier EA101, a current source Ir101, a reference voltage source V101, and a phase compensation terminal T102. A parasitic capacitor Cp101 is generated at the phase compensation terminal T102. The phase compensation circuit COMP101 includes a phase compensation resistor Rc101 and a phase compensation capacitor Cc101.
As shown in FIG. 1, the phase compensation resistor Rc101 and the phase compensation capacitor Cc101 are connected in series between the phase compensation terminal T102 and the ground terminal. In addition, a reference voltage Vref1 generated in the reference voltage source V101 is applied to a non-inverting input terminal (+) of the error amplifier EA101, and an input voltage (feedback voltage) Vfb101 is applied to an inverting input terminal (−) of the error amplifier EA101. An output terminal (error-voltage output terminal) T111 of the error amplifier EA101 is connected to the phase compensation terminal T102.
In the error amplification circuit 110a shown in FIG. 1, the current source Ir101 generates a predetermined bias current Ibias101 for supply to the error amplifier EA101. The error amplifier EA101 amplifies a difference between the reference voltage Vref1 and the input voltage Vfb101 for output as an error voltage Ve101 to a next stage of the circuit via the output terminal T111 thereof. In addition, the phase compensation circuit COMP101 compensates for phase in the error amplifier EA101.
Since the error amplification circuit 110a shown in FIG. 1 includes the external phase compensation resistor Rc101 in the phase compensation circuit COMP101 that is provided outside the integrated circuit 110, by changing the resistance of the phase compensation resistor Rc101a gain in a high-frequency range of the error voltage Ve101 output from the error amplifier EA101 can be controlled externally. Therefore, it is not necessary to control the bias current Ibias so as to control the high-frequency gain of the error voltage Ve101. By contrast, since the parasitic capacitor Cp101 generated in the error amplifier EA101 is connected to the output terminal T111 of the error amplifier EA101, the error amplifier EA101 is directly affected by the parasitic capacitor Cp101, making it necessary to design the error amplifier EA101 in accordance with the configuration of the error amplification circuit 110a. 
As described above, in order to suit the external phase compensation method, the impedance of the external phase compensation circuit COMP101 is set smaller than the parasitic capacitor Cp101 of the phase compensation terminal T102, and the output resistance of the error amplifier EA101 is set sufficiently small to suit the external phase compensation circuit COMP101, which enormously increases both the size of the circuit and the consumption of current in the circuit compared to an error amplification circuit with a built-in phase compensation circuit.